Accurate Depth of Radiofrequency-Induced Lesions in Renal Sympathetic Denervation Based on a Fine Histological Sectioning Approach in a Porcine Model

Abstract

Background—Ablation lesion depth caused by radiofrequency-based renal denervation (RDN) was limited to <4 mm in previous animal studies, suggesting that radiofrequency-RDN cannot ablate a substantial percentage of renal sympathetic nerves. We aimed to define the true lesion depth achieved with radiofrequency-RDN using a fine sectioning method and to investigate biophysical parameters that could predict lesion depth.Methods and Results—Radiofrequency was delivered to 87 sites in 14 renal arteries from 9 farm pigs at various ablation settings: 2, 4, 6, and 9 W for 60 seconds and 6 W for 120 seconds. Electric impedance and electrode temperature were recorded during ablation. At 7 days, 2470 histological sections were obtained from the treated arteries. Maximum lesion depth increased at 2 to 6 W, peaking at 6.53 (95% confidence interval, 4.27–8.78) mm under the 6 W/60 s condition. It was not augmented by greater power (9 W) or longer duration (120 seconds). There were statistically significant tendencies at 6 and 9 W, with higher injury scores in the media, nerves, arterioles, and fat. Maximum lesion depth was positively correlated with impedance reduction and peak electrode temperature (Pearson correlation coefficients were 0.59 and 0.53, respectively).Conclusions—Lesion depth was 6.5 mm for radiofrequency-RDN at 6 W/60 s. The impedance reduction and peak electrode temperature during ablation were closely associated with lesion depth. Hence, these biophysical parameters could provide prompt feedback during radiofrequency-RDN procedures in the clinical setting.

Safety of catheter‐based radiofrequency renal denervation on branch renal arteries in a porcine model

“…However, the present study showed that electrode temperature in the branch RA (66.2°C) was equivalent to that in main RA (64.2°C), and there was no increase in histopathological arterial damage in the branch RA. The equivalent electrode temperature was likely a result of the automatic control mechanism of the IberisBloom system, which decreases output power when electrode temperature reaches ≥70°C, as shown by the significantly lower terminal output power in the branch RA compared with the main RA . However, impedance was higher when the electrode was located in the branch RA than in the main RA.…”

“…First, the findings obtained from the normotensive swine may not be applicable to patients with hypertension. However, the normotensive swine is the standard animal model for assessing RDN device safety, because of its anatomical and physiological similarity to humans . Second, because of the small number of animals, adverse findings with a low incidence may have been missed.…”

“…The IberisBloom RDN system (Terumo Corporation, Tokyo, Japan) used in the present study consists of a helical multi‐electrode catheter and a multi‐channel generator, as previously described . The generator delivers RF (with 6 W for 60 sec) to selected electrodes simultaneously.…”

“…The equivalent electrode temperature was likely a result of the automatic control mechanism of the IberisBloom system, which decreases output power when electrode temperature reaches ≥70 C, as shown by the significantly lower terminal output power in the branch RA compared with the main RA. 25 However, impedance was higher when the electrode was located in the branch RA than in the main RA. Generally, a higher impedance relates to an increased contact force of an electrode to local tissues.…”

“…The IberisBloom RDN system (Terumo Corporation, Tokyo, Japan) used in the present study consists of a helical multi-electrode catheter and a multi-channel generator, as previously described. 25 The generator delivers RF (with 6 W for 60 sec) to selected electrodes simultaneously. The IberisBloom system has an automatic algorithm that decreases output power by 1 W in the channel when the corresponding electrode temperature is ≥70 C for 1 sec.…”